Electronic module with integrated programmable thermoelectric cooling assembly and method of fabrication

ABSTRACT

An electronic module and method of fabrication are provided employing an integrated thermal dissipation assembly. The thermal dissipation assembly includes a thermoelectric assembly configured to couple to an electronic device within the module for removing heat generated thereby, and a programmable power control circuit integrated with the thermoelectric assembly. The programmable power control circuit allows cooling capacity of the thermoelectric assembly to be tailored to anticipated heat dissipation of the electronic device by adjusting, for a given power source, voltage level to the thermoelectric elements of the thermoelectric assembly. Power to the thermoelectric assembly can be provided through conductive power planes disposed within a supporting substrate. The power control circuit includes one or more voltage boost circuits connected in series between the given power source and the thermoelectric elements of the associated thermoelectric assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/726,909, filed Nov. 30, 2000 now U.S. Pat. No. 6,548,894, entitled“Electronic Module With Integrated Programmable Thermoelectric CoolingAssembly and Method of Fabrication”, the entirety of which is herebyincorporated herein by reference.

This application also contains subject matter which is related to thesubject matter of the following applications, which are assigned to thesame Assignee as this application. The below-listed applications arehereby incorporated herein by reference in their entirety:

“ELECTRONIC MODULE WITH INTEGRATED THERMOELECTRIC COOLING ASSEMBLY,” byChu et al., U.S. Pat. No. 6,489,551, issued Dec. 3, 2002;

“THERMOELECTRIC COOLING ASSEMBLY WITH THERMAL SPACE TRANSFORMERINTERPOSED BETWEEN CASCADED THERMOELECTRIC STAGES FOR IMPROVED THERMALPERFORMANCE,” by Chu et al., U.S. Pat. No. 6,164,076, issued Dec. 26,2000;

“THERMOELECTRIC-ENHANCED HEAT SPREADER FOR HEAT GENERATING COMPONENT FORAN ELECTRONIC DEVICE,” by Chu et al, U.S. Pat. No. 6,424,533, issuedJul. 23, 2002; and

“THERMAL SPREADER AND INTERFACE ASSEMBLY FOR HEAT GENERATING COMPONENTOF AN ELECTRONIC DEVICE,” by Chu et al., U.S. Pat. No. 6,396,700, issuedMay 28, 2002.

TECHNICAL FIELD

The present invention is directed to cooling assemblies and otherapparatus used for removing heat from electronic devices. Moreparticularly, the present invention is directed to an electronic modulewith integrated thermoelectric cooling elements. Even more particularly,this invention is directed to an enhanced thermoelectric apparatushaving an integrated power control circuit which provides a programmablevoltage level from a given power source, to allow customization of thecooling capacity of the thermoelectric assembly when the thermoelectricassembly is interposed within an electronic module in thermal contactwith a heat generating component thereof, such as an integrated circuitchip.

BACKGROUND OF THE INVENTION

As is well known, as the circuit density of electronic chip devicesincreases, there is a correspondingly increasing demand for the removalof heat generated by these devices. The increased heat demand arisesboth because the circuit devices are packed more closely together andbecause the circuits themselves are operated at increasingly high clockfrequencies. Nonetheless, it is also known that runaway thermalconditions and excessive heat generated by chips is a leading cause forfailure of chip devices. Furthermore, it is anticipated that the demandfor heat removal for these devices will increase indefinitely.Accordingly, it is seen that there is a large and significant need toprovide useful cooling mechanisms for electronic circuit devices.

Thermoelectric cooling elements operate electronically to produce acooling effect. By passing a direct current through the legs of athermoelectric device, a temperature difference is produced across thedevice which is contrary to that which would be expected from Fourier'sLaw.

At one junction of the thermoelectric element both holes and electronsmove away, toward the other junction, as a consequence of the currentflow through the junction. Holes move through the p-type material andelectrons through the n-type material. To compensate for this loss ofcharge carriers, additional electrons are raised from the valence bandto the conduction band to create new pairs of electrons and holes. Sinceenergy is required to do this, heat is absorbed at this junction.Conversely, as an electron drops into a hole at the other junction, itssurplus energy is released in the form of heat. This transfer of thermalenergy from the cold junction to the hot junction is known as thePeltier effect.

Use of the Peltier effect permits the surfaces attached to a heat sourceto be maintained at a temperature below that of a surface attached to aheat sink. What these thermoelectric modules provide is the ability tooperate the cold side below the ambient temperature of the coolingmedium (air or water) or provide greater heat removal capacity for agiven cold plate or component temperature. When direct current is passedthrough these thermoelectric modules a temperature difference isproduced with the result that one side is relatively cooler than theother side. These thermoelectric modules are therefore seen to possess ahot side and a cold side, and provide a mechanism for facilitating thetransfer of thermal energy from the cold side of the thermoelectricmodule to the hot side of the module.

SUMMARY OF THE INVENTION

Conventional configurations and positionings of thermoelectricassemblies are nonetheless seen herein to be unnecessarily limiting interms of the thermal energy which may be transferred and the long termreliability attained. Thus, while the use of thermoelectric devices isseen to provide a means for the solid state cooling of adjacentelectrical devices, their efficiency and reliability has been less thanoptimal.

In addition, as complementary metal oxide semiconductor (CMOS) circuitand process technologies approach scaling limits, it becomes necessaryto seek approaches and opportunities to achieve further performancegains. One avenue which is receiving increased attention is theoperation of CMOS circuits at lower temperatures. The circuitperformance enhancements which may be achieved vary from about 1.1x at acooling condition of 250° C., to 18x at a cooling condition of −200° C.To obtain cooling conditions down to about 50° C. or so, conventionalrefrigeration technology may be utilized. However, conventionalrefrigeration systems may be difficult to control for variations in heatload, and may not be responsive enough during transient operatingconditions.

Thermoelectric devices, used in conjunction with other module coolingtechnologies, are known to be able to lower junction temperatures belowthat which can be achieved by the other module cooling technologiesalone. Problems arise, however, when thermoelectric devices are takendown in temperature below the ambient, and in particular, below theenvironment dew point temperature. Traditionally, thermoelectricdevices, which are separate from and attached to an electronic modulecasing (i.e., cap) are exposed to the system environment. When broughtdown in temperature below the dew point, condensation forms. Thiscondensation significantly reduces the fatigue life due to corrosion ofthe solder joints forming the thermoelectric junctions. In fact, themere presence of oxygen accelerates solder fatigue cracking.

Advantageously, disclosed herein is a means for improving thermoelectricdevice reliability when used in conjunction with cooling of electronicmodules. Specifically, a thermoelectric apparatus is integrated withinan electronic module itself so that the thermoelectric apparatus ismaintained in a controlled, i.e., oxygen and moisture restricted,environment. Furthermore, by integrating a thermoelectric apparatus intothe electronic module, power delivery to the thermoelectric devices canbe integrated with the module, thus simplifying system level design,i.e., in comparison with delivering power to externally mountedthermoelectric devices.

Further, disclosed herein is the use of thin-film integratedthermoelectric assemblies as a means of achieving reduced temperatureson individual chips within a multi-chip module (MCM). The conventionalapproach to cooling a multi-chip module is to sandwich a largethermoelectric cooler between the top surface of the MCM and a heatsink. While this approach works for a single chip module with a singleheat source, it is not believed satisfactory for a multi-chip modulewith chips dissipating different amounts of heat. The thermoelectricjunctions over the high heat dissipating chips would be over-loaded andthose over the lower power chips would be underutilized. The resultwould be a higher temperature than desired on the higher dissipatingchips (i.e., higher power chips) and lower than desired temperatures onthe lower heat dissipating chips (i.e., lower power chips). The presentinvention addresses this problem by integrating a discrete thin-filmthermoelectric assembly atop each chip within a multi-chip module, andfurther by making these individual thermoelectric assembliesprogrammable by tailoring the voltage level available to eachthermoelectric assembly. This tailoring of the thermoelectric assemblyis achieved without adjusting the number, size and geometry of thethermoelectric elements to match the individual cooling capacity of theassociated chip heat load. Thus, the present invention accomplishesprogrammable thermoelectric cooling using a common thermoelectric devicedesign.

To summarize, in one aspect, presented is a thermal dissipation assemblyfor an electronic device. The dissipation assembly includes athermoelectric assembly configured to couple to the electronic devicefor removing heat generated thereby, and a programmable power controlcircuit. The programmable power control circuit is integrated with thethermoelectric assembly and allows cooling capacity of thethermoelectric assembly to be tailored to anticipated heat dissipationof the electronic device by adjusting, for a given power source, voltagelevel to the thermoelectric elements of the thermoelectric assembly. Anelectronic circuit and multi-chip module employing the thermaldissipation assembly are also described and claimed herein.

Further, in another aspect, a method of fabricating an electroniccircuit is presented which includes: providing at least one electronicdevice; thermally coupling at least thermoelectric assembly to the atleast one electronic device, wherein each thermoelectric assemblyincludes a programmable power control circuit for adjusting, for a givenpower source, voltage level to thermoelectric elements thereof;connecting the given power source to the at least one thermoelectricassembly through the programmable power control circuit; and employingthe programmable power control circuit to tailor the voltage level tothe thermoelectric elements of the at least one thermoelectric assembly,the tailoring being based upon anticipated heat dissipation of the atleast one electronic device to which the at least one thermoelectricassembly is thermally coupled.

As a further enhancement, by integrating thermoelectric coolingassemblies within the electronic module, power delivery to thethermoelectric elements can be simplified by eliminating discrete wiringoutside of the module. Wire bond or electrical spring contacts can beemployed within the module to couple the thermoelectric stages toappropriate power planes, e.g., disposed within the substrate of themodule.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered part of the claimedinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-described objects, advantages and features of the presentinvention, as well as others, will be more readily understood from thefollowing detailed description of certain preferred embodiments of theinvention, when considered in conjunction with the accompanying drawingin which:

FIG. 1 is an elevational view illustrating one embodiment of amulti-chip module (MCM) employing integrated thermoelectric assembliesin accordance with the principles of the present invention;

FIG. 2 is a partial elevational view illustrating one embodiment of aprogrammable thermoelectric cooling assembly in accordance with theprinciples of the present invention;

FIG. 2A is cross-sectional plan view of FIG. 2 taken along line A—A;

FIG. 3A depicts one embodiment of a programmable power control circuitto be integrated in a thermoelectric cooling assembly in accordance withthe principles of the present invention; and

FIGS. 3B-3E depict various programmed configurations of the powercontrol circuit of FIG. 3A attained using various laser delete patternsas shown.

BEST MODE FOR CARRYING OUT THE INVENTION

Generally stated, provided herein is an electronic module with anintegrated thermoelectric cooling assembly for removing heat from anelectronic device thereof, such as an integrated circuit chip. Thethermoelectric cooling assembly and electronic device are sealedtogether within the module, for example, between a substrate and athermally conductive cap. In one embodiment, a module comprises amulti-chip module (MCM) wherein each electronic device within the modulehas coupled thereto a programmable thermoelectric cooling assembly inaccordance with the present invention. Each programmable thermoelectriccooling assembly has a same number and geometry of thermoelectricelements, but can be tailored (i.e., programmed) through a power controlcircuit integrated into each thermoelectric assembly. For example, thepower control circuit may comprise a series of voltage boost circuitswhich (using laser delete techniques) may be added or removed to adjusta voltage level to each thermoelectric assembly based upon anticipatedheat dissipation of the corresponding electronic device within themulti-chip module.

FIG. 1 depicts one embodiment of an electronic module, generally noted10, in accordance with the principles of the present invention. Althoughdepicted in FIG. 1 and described hereinbelow with reference to amulti-chip module having a single thermoelectric cooling stage coupledto each chip, the programmable thermoelectric assembly of the presentinvention could equally be applicable to an electronic module having asingle electronic device with, e.g., one or more thermoelectric stagesthermally coupled thereto.

In the embodiment of FIG. 1, module 10 comprises a multi-chip module(MCM) wherein three electronic devices 12, (for example, integratedcircuit chips) are mounted on a substrate 14 and electrically connectedto circuitry on or within substrate 14 via conventional metalconnections, such as solder bumps 16. A separate thermoelectric coolingassembly 20 is thermally coupled to each different electronic device 12within the module. Further, each thermoelectric cooling assembly 20 isthermally coupled, for example, by means of a thermal paste or grease,to a module cap 26. The total module heat load, including the powerdissipation of the thermoelectric cooling assemblies, can be removed bymeans of a heat sink or cold plate (not shown) attached to the exposedsurface of module cap 26.

As noted above, it is well known that by passing direct current througha series of thermoelectric couples, one side of the thermoelectric willtransfer heat to the other side. Essentially, heat is “electronically”pumped from the cold side to the hot side. In the embodiment of FIG. 1,the cold side of each cooling assembly is thermally coupled to an uppersurface of an electronic device 12, for example, employing anappropriate oil or phase change interface material, such as Chomerics'Thermflow™ T310 material marketed by Parker Hannifin Corporation ofWoburn, Mass.

Heat which flows out the hot side of a set of thermoelectric coupleswill be comprised of the active heat pumped, in addition to the powerdissipation of the thermoelectric couples in performing the electronicheat pumping action. In this example, heat flows through thethermoelectric assembly 20 to thermal grease 27 and thereafter tothermally conductive cap 26, which as noted may be coupled to a coldplate (not shown).

As an alternative embodiment, one or more of the thermoelectric coolingassemblies 20 could comprise a multi-stage cooling assembly employingtwo or more cascaded thermoelectric stages with a lightweight “thermalspace transformer” disposed therebetween to distribute heat from a firststage to a second stage. Such an assembly is described in detail in theabove-incorporated United States Patent Application entitled,“THERMOELECTRIC COOLING ASSEMBLY WITH THERMAL SPACE TRANSFORMERINTERPOSED BETWEEN CASCADED THERMOELECTRIC STAGES FOR IMPROVED THERMALPERFORMANCE,” Ser. No. 09/368,803.

In the embodiment of FIG. 1, each thermoelectric assembly 20 maycomprise a thin-film thermoelectric assembly, such as described in oneor more of U.S. Pat. Nos. 6,043,423 and 6,127,619, as well as thefollowing articles: Fleurial et al., “Thermoelectric Microcoolers ForThermal Management Applications”, 16th International Conference onThermoelectrics, IEEE (1997), Fleurial et al., “Thick-FilmThermoelectric Microdevices”, 18th International Conference onThermoelectrics (1999), and Vandersande et al., “Thermal Management ofPower Electronics Using Thermoelectric Coolers”, 15th InternationalConference on Thermoelectrics (1996), each of which is herebyincorporated herein by reference in its entirety.

Each thermoelectric assembly includes a lower support plate 22 and anupper support plate 24 between which the thermoelectric couples orelements are disposed. Each lower support plate 22 has a larger surfacearea than the corresponding upper support plate 24. This larger surfacearea facilitates wire bonding 30 between pads on the upper surface ofsubstrate 14 and appropriate landing pads 60 (FIG. 2A) on lower supportplate 22 of each assembly. FIG. 2A is a cross-sectional plan view of thethermoelectric assembly of FIG. 2.

In one embodiment, the lower and upper support plates 22 and 24 of eachthermoelectric assembly may comprise silicon. Thin-film bismuthtelluride “N” and “P” thermoelectric elements are deposited on thesilicon substrate. Appropriate insulating layers 42 and 44, such assilicon dioxide, separate the electrically conductive thermoelectricelements from the respective supporting silicon substrates 22 and 24.The use of silicon (or other semiconductor material) as a carrierfacilitates attachment of the thermoelectric assembly to an integratedcircuit chip (such as device 12 of FIG. 1, which may also be fabricatedof silicon), using either a solder joint or thermal epoxy. A solderjoint offers the advantage of low thermal resistance between the chipand the associated thermoelectric assembly.

The silicon support plates of FIGS. 2 and 2A provide mechanical supportto the thermoelectric elements, but also accommodate a specializedintegrated circuit in accordance with the present invention. Thisspecialized circuit provides a mechanism for customizing the heat loadcapacity of each thermoelectric assembly for the associated integratedcircuit chip to be cooled. As shown in FIG. 2A, conductive lines aredeposited on the silicon carrier for the purpose of distributingelectrical current to and interconnecting the thermoelectric elements 50(FIG. 2). Although not shown, a similar pattern of conductive lines andpads would be provided on the underside of the upper support plate 24 ofeach thermoelectric assembly.

In this embodiment, the lower support substrate is shown to accommodatethe programmable voltage boost circuit 70 in accordance with the presentinvention. By using programmable voltage boost circuitry as describedhereinbelow, electrical power provided to the integrated thermoelectriccooling assemblies from a given power source, such as a power planedisposed within substrate 14, can be tailored for each thermoelectricassembly to allow adjusting of the assembly's cooling effect givendifferences in the heat generation capability of the differentelectronic devices to which the assemblies are thermally coupled. In oneembodiment, an integrated power control circuit 70 is incorporated on atleast one silicon carrier of each thermoelectric assembly between thesupply voltage wiring pads 60 and the current distribution lines 45 (seeFIG. 2A).

FIG. 3A depict one functional diagram of a power control circuit 70 inaccordance with the present invention. In this implementation, eachon-carrier power control circuit 70 includes voltage boost circuit 71,72 and 73 wired in series between the power supply (for example, 1.5volts) and the load (i.e., thermoelectric elements). Wiring shunt linesare also provided parallel to each voltage boost circuit. Examples ofways in which these voltage booster circuit can be used to customize thevoltage applied to a thermoeletric cooling chip are depicted in FIGS.3B-3E. For purposes of this example, it is assumed that each voltageboost circuit represented by blocks 71, 72 and 73 will provide a similarvoltage boost, for example, 1.5x. By making appropriate laser deletioncuts, “x” in the wiring lines, it is possible for different voltagelevels varying from 1.5 to 5.06 volts (for example) to be provided asshown in FIGS. 3B-3E. This comprises a practical means of obtainingdifferent cooling capacities from a single thermoelectric assemblydesign and a single substrate voltage source. Those skilled in the artwill note that the number of boost circuits maybe less or more dependingupon the range and granularity desired for the thermoelectric assembly.By way of example, boost circuits are described in a textbook by RobertW. Erickson, entitled, “Fundamentals of Power Electronics”, published byKluwer Academic Publishers, pp. 24 & 138 (1997), which is herebyincorporated herein by reference in its entirety.

Additionally, if desired, a microprocessor cooling system controllercould monitor the electronic module temperature by a thermistor, forexample, mounted within the module housing. A thermistor sense linewould be fed back to the cooling system controller. If the moduletemperature changes, the controller can then provide a signal to a dcpower controller to universally increase or decrease electric current toall thermoelectric cooling assemblies as required to quickly return themodule to a set point condition or range.

Advantageously, by disposing multiple thermoelectric cooling assemblieswithin an electronic module, the electronic device and coolingassemblies are maintained in a controlled, i.e., oxygen and moisturefree environment. Further, disclosed hereinabove is the use of thin-filmintegrated thermoelectric assemblies as a means of achieving reducedtemperatures on individual chips within an multi-chip module. Thepresent invention allows customizing thermoelectric cooling of higherdissipating chips compared with lower dissipating chips by programmingthe voltage level to be applied to the respective assembly. Thistailoring of the thermoelectric assembly is achieved without adjustingthe number, size or geometry of the thermoelectric elements to match theindividual cooling capacity of the associated chip heat load. Thepresent invention accomplishes programmable thermoelectric cooling usinga common thermoelectric device design.

While the invention has been described in detail herein in accordancewith certain preferred embodiments thereof, many modifications andchanges therein may be effected by those skilled in the art.Accordingly, it is intended by the appended claims to cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

What is claimed is:
 1. A method for fabricating an electric circuitcomprising: providing at least one electronic device; coupling at leastone thermoelectric assembly to said at least one electronic device,wherein each thermoelectric assembly includes a statically tailorablepower control circuit for selecting, for a given power source, a voltagelevel to thermoelectric elements thereof from a plurality of selectablevoltage levels; connecting said given power source to said at lest onethermoelectric assembly through said programmable power control circuit;and employing said statically tailorable power control circuit toinitially tailor the voltage level to thermoelectric elements of said atleast one thermoelectric assembly, said tailoring being based uponanticipated heat dissipation of said at least one electronic device towhich said at least one thermoelectric assembly is thermally coupled. 2.A method for fabricating an electric circuit comprising: providing atleast one electronic device: thermally coupling at least onethermoelectric assembly to said at least one electronic device, whereineach thermoelectric assembly includes a programmable power controlcircuit for adjusting, from a given power source, voltage level tothermoelectric elements thereof; connecting said given power source tosaid at lest one thermoelectric assembly through said programmable powercontrol circuit; employing said programmable power control circuit totailor the voltage level to thermoelectric elements of said at least onethermoelectric assembly, said tailoring being based upon anticipatedheat dissipation of said at least one electronic device to which said atleast one thermoelectric assembly is thermally coupled; and furthercomprising mounting the at least one electronic device on a substrate,and wherein said given power source comprises at least one power planewithin said substrate.
 3. A method for fabricating an electric circuitcomprising: providing at least one electronic device; thermally couplingat least one thermoelectric assembly to said at least one electronicdevice, wherein each thermoelectric assembly includes a programmablepower control circuit for adjusting, from a given power source, voltagelevel to thermoelectric elements thereof; connecting said given powersource to said at lest one thermoelectric assembly through saidprogrammable power control circuit; employing said programmable powercontrol circuit to tailor the voltage level to thermoelectric elementsof said at least one thermoelectric assembly, said tailoring being basedupon anticipated heat dissipation of said at least one electronic deviceto which said at least one thermoelectric assembly is thermally coupled;and wherein each said programmable power control circuit comprises atleast one voltage boost circuit connected in series between said givenpower source and said thermoelectric elements of its respectivethermoelectric assembly, each voltage boost circuit having a wiringshunt line in parallel therewith, and wherein said employing comprisesopen circuiting a conductive line to or from said at least one voltageboost circuit or said wiring shunt line in parallel therewith to tailorsaid voltage level supplied to said thermoelectric elements.
 4. Themethod of claim 3, wherein said open circuiting comprises laser deletinga portion of said conductive line to or from said at least one voltageboost circuit or said wiring shunt line in parallel therewith.
 5. Amethod for fabricating an electric circuit comprising: providing atleast one electronic device; thermally coupling at least onethermoelectric assembly to said at least one electronic device, whereineach thermoelectric assembly includes a programmable power controlcircuit for adjusting, from a given power source, voltage level tothermoelectric elements thereof; connecting said given power source tosaid at lest one thermoelectric assembly through said programmable powercontrol circuit; employing said programmable power control circuit totailor the voltage level to thermoelectric elements of said at least onethermoelectric assembly, said tailoring being based upon anticipatedheat dissipation of said at least one electronic device to which said atleast one thermoelectric assembly is thermally coupled; and wherein saidproviding comprises providing multiple electronic devices, eachelectronic device comprising an integrated circuit chip, and whereinsaid thermally coupling comprises thermally coupling a differentthermoelectric assembly to each integrated circuit chip of said multipleintegrated circuit chips, wherein at least one integrated circuit chipof said multiple integrated circuit chips dissipates a greater amount ofheat when operational, and wherein said employing comprises tailoringthe voltage level to thermoelectric elements of said thermoelectricassembly associated with said at least one integrated circuit chipdissipating said greater amount of heat to increase the voltage level tosaid thermoelectric elements, thereby enhancing cooling of saidintegrated circuit chip dissipating said greater amount of heat.
 6. Themethod of claim 1, further comprising providing a thermally conductivecap and sealing said thermally conductive cap to said substrate suchthat said at least one thermoelectric assembly is disposed between saidat least one electronic device and said thermally conductive cap and isin thermal contact with said thermally conductive cap.